Special Issue "Complex Concentrated Alloys (CCAs) - Current Understanding and Future Opportunities"

A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: 31 December 2019.

Special Issue Editor

Guest Editor
Dr. Sundeep Mukherjee

Department of Materials Science and Engineering, University of North Texas, 1155 Union Circle, Denton, TX 76203, USA
Website | E-Mail
Interests: metals and alloys; HEAs; BMGs; mechanical behavior and corrosion behavior

Special Issue Information

Dear Colleagues,

This Special Issue aims to present recent developments and future opportunities related to the topic of complex concentrated and high entropy alloys from fundamental aspects to various applications. Conventional structural alloys are single principal element systems with multi-phase microstructures. In that regard, complex concentrated alloys (CCAs), with multiple principal elements, represent a new paradigm in alloy design by focusing on the central region of a multi-component phase space rather than the edges. High configurational entropy leads to single-phase solid solutions in a certain subset of these multi-principal element systems, which have been termed as high entropy alloys (HEAs). However, the focus on a single-phase microstructure severely limits performance in real-world engineering applications. CCAs retain the “high entropy” nature of the parent matrix and add complex precipitates containing multiple elements on their respective sub-lattices as strengtheners. The core effects of high configurational entropy, lattice distortion and sluggish diffusion lead to a gamut of attractive properties including high strength-ductility combination, resistance to oxidation, corrosion/wear resistance, and interesting magnetic properties. For this Special Issue, contributions are welcome from experimentalists, theorists, and computational scientists in this field.

Specific topics of interest include (but are not limited to):

  • Thermodynamics, kinetics, and phase transformation in multi-phase CCAs
  • Mechanical behavior and deformation mechanisms
  • Microstructure evolution as a function of processing
  • Tribology, corrosion and oxidation behavior
  • Magnetic and magneto-caloric properties
  • Irradiation effects
  • High strain-rate deformation behavior
  • Simulation and modeling including DFT, MD, Phase-field, and CALPHAD

Prof. Dr. Sundeep Mukherjee
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Metals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1500 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Complex Concentrated Alloys
  • High Entropy Alloys
  • Alloy Design
  • Mechanical Behavior
  • Magnetic Properties
  • Irradiation Effects

Published Papers (6 papers)

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Research

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Open AccessArticle
Gradient Distribution of Microstructures and Mechanical Properties in a FeCoCrNiMo High-Entropy Alloy during Spark Plasma Sintering
Metals 2019, 9(3), 351; https://doi.org/10.3390/met9030351
Received: 31 January 2019 / Revised: 12 March 2019 / Accepted: 15 March 2019 / Published: 19 March 2019
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Abstract
A novel graded material of a high-entropy alloy (HEA) FeCoCrNiMo was fabricated by spark plasma sintering (SPS) processing. After SPS, the HEA specimens consisted of a single face-centred cubic (FCC) phase in the center, but dual FCC and a tetragonal structure σ phase [...] Read more.
A novel graded material of a high-entropy alloy (HEA) FeCoCrNiMo was fabricated by spark plasma sintering (SPS) processing. After SPS, the HEA specimens consisted of a single face-centred cubic (FCC) phase in the center, but dual FCC and a tetragonal structure σ phase near the surface. Surprisingly, the sintering pressure was sufficient to influence the proportion of phases, and thus the properties of HEA samples. The hardness of the specimens sintered under the pressures of 30, 35, and 40 MPa increased gradually from 210 HV0.2, which is the single FCC phase in the center, to the maximum value near the surface as a result of the gradual increase in the fraction of the transformed σ phase. The σ phase, being a complex hard and brittle intermetallic particle to manipulate the properties of FCC-type HEA systems, which could be influenced by pressure, indicated a major possibility for designing gradient HEA materials. Full article
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Open AccessArticle
Activation Volume and Energy for Dislocation Nucleation in Multi-Principal Element Alloys
Metals 2019, 9(2), 263; https://doi.org/10.3390/met9020263
Received: 25 January 2019 / Revised: 19 February 2019 / Accepted: 21 February 2019 / Published: 23 February 2019
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Abstract
Incipient plasticity in multi-principal element alloys, CoCrNi, CoCrFeMnNi, and Al0.1CoCrFeNi was evaluated by nano-indentation and compared with pure Ni. The tests were performed at a loading rate of 70 μN/s in the temperature range of 298 K to 473 K. The [...] Read more.
Incipient plasticity in multi-principal element alloys, CoCrNi, CoCrFeMnNi, and Al0.1CoCrFeNi was evaluated by nano-indentation and compared with pure Ni. The tests were performed at a loading rate of 70 μN/s in the temperature range of 298 K to 473 K. The activation energy and activation volume were determined using a statistical approach of analyzing the “pop-in” load marking incipient plasticity. The CoCrFeMnNi and Al0.1CoCrFeNi multi-principal element alloys showed two times higher activation volume and energy compared to CoCrNi and pure Ni, suggesting complex cooperative motion of atoms for deformation in the five component systems. The small calculated values of activation energy and activation volume indicate heterogeneous dislocation nucleation at point defects like vacancy and hot-spot. Full article
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Graphical abstract

Open AccessArticle
Preparation and Performance Analysis of Nb Matrix Composites Reinforced by Reactants of Nb and SiC
Metals 2018, 8(4), 233; https://doi.org/10.3390/met8040233
Received: 5 February 2018 / Revised: 22 March 2018 / Accepted: 27 March 2018 / Published: 3 April 2018
Cited by 2 | PDF Full-text (25906 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, one kind of new composite material formed with Nb and SiC was prepared by hot pressing sintering. The influence of the addition of SiC particles on the mechanical properties at room and high temperature was analyzed. The composite material consists [...] Read more.
In this paper, one kind of new composite material formed with Nb and SiC was prepared by hot pressing sintering. The influence of the addition of SiC particles on the mechanical properties at room and high temperature was analyzed. The composite material consists of three phases: Nb2C, Nb3Si, and Nb solid solution (Nbss). The fraction of SiC particles added in the Nb matrix was 3%, 5%, and 7%, respectively. Flexural strength, Vickers hardness, and compressive strength at room temperature were improved with the increasing of SiC content. Among them, compressive strength and fracture toughness were higher than those of Nb/Nb5Si3 composites. The compressive strength at high temperature of the new composites was higher than that of Nb-Si alloys, which improved with the increasing of SiC content. Full article
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Open AccessArticle
Slurry Erosion Behavior of AlxCoCrFeNiTi0.5 High-Entropy Alloy Coatings Fabricated by Laser Cladding
Metals 2018, 8(2), 126; https://doi.org/10.3390/met8020126
Received: 7 January 2018 / Revised: 4 February 2018 / Accepted: 5 February 2018 / Published: 11 February 2018
Cited by 3 | PDF Full-text (3890 KB) | HTML Full-text | XML Full-text
Abstract
High-entropy alloys (HEAs) have gained extensive attention due to their excellent properties and the related scientific value in the last decade. In this work, AlxCoCrFeNiTi0.5 HEA coatings (x: molar ratio, x = 1.0, 1.5, 2.0, and 2.5) were [...] Read more.
High-entropy alloys (HEAs) have gained extensive attention due to their excellent properties and the related scientific value in the last decade. In this work, AlxCoCrFeNiTi0.5 HEA coatings (x: molar ratio, x = 1.0, 1.5, 2.0, and 2.5) were fabricated on Q345 steel substrate by laser-cladding process to develop a practical protection technology for fluid machines. The effect of Al content on their phase evolution, microstructure, and slurry erosion performance of the HEA coatings was studied. The AlxCoCrFeNiTi0.5 HEA coatings are composed of simple face-centered cubic (FCC), body-centered cubic (BCC) and their mixture phase. Slurry erosion tests were conducted on the HEA coatings with a constant velocity of 10.08 m/s and 16–40 meshs and particles at impingement angles of 15, 30, 45, 60 and 90 degrees. The effect of three parameters, namely impingement angle, sand concentration and erosion time, on the slurry erosion behavior of AlxCoCrFeNiTi0.5 HEA coatings was investigated. Experimental results show AlCoCrFeNiTi0.5 HEA coating follows a ductile erosion mode and a mixed mode (neither ductile nor brittle) for Al1.5CoCrFeNiTi0.5 HEA coating, while Al2.0CoCrFeNiTi0.5 and Al2.5CoCrFeNiTi0.5 HEA coatings mainly exhibit brittle erosion mode. AlCoCrFeNiTi0.5 HEA coating has good erosion resistance at all investigated impingement angles due to its high hardness, good plasticity, and low stacking fault energy (SFE). Full article
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Review

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Open AccessReview
A Review of Multi-Scale Computational Modeling Tools for Predicting Structures and Properties of Multi-Principal Element Alloys
Metals 2019, 9(2), 254; https://doi.org/10.3390/met9020254
Received: 14 January 2019 / Revised: 2 February 2019 / Accepted: 9 February 2019 / Published: 20 February 2019
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Abstract
Multi-principal element (MPE) alloys can be designed to have outstanding properties for a variety of applications. However, because of the compositional and phase complexity of these alloys, the experimental efforts in this area have often utilized trial and error tests. Consequently, computational modeling [...] Read more.
Multi-principal element (MPE) alloys can be designed to have outstanding properties for a variety of applications. However, because of the compositional and phase complexity of these alloys, the experimental efforts in this area have often utilized trial and error tests. Consequently, computational modeling and simulations have emerged as power tools to accelerate the study and design of MPE alloys while decreasing the experimental costs. In this article, various computational modeling tools (such as density functional theory calculations and atomistic simulations) used to study the nano/microstructures and properties (such as mechanical and magnetic properties) of MPE alloys are reviewed. The advantages and limitations of these computational tools are also discussed. This study aims to assist the researchers to identify the capabilities of the state-of-the-art computational modeling and simulations for MPE alloy research. Full article
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Open AccessFeature PaperReview
Corrosion, Erosion and Wear Behavior of Complex Concentrated Alloys: A Review
Metals 2018, 8(8), 603; https://doi.org/10.3390/met8080603
Received: 18 June 2018 / Revised: 18 July 2018 / Accepted: 24 July 2018 / Published: 3 August 2018
Cited by 2 | PDF Full-text (25021 KB) | HTML Full-text | XML Full-text
Abstract
There has been tremendous interest in recent years in a new class of multi-component metallic alloys that are referred to as high entropy alloys, or more generally, as complex concentrated alloys. These multi-principal element alloys represent a new paradigm in structural material design, [...] Read more.
There has been tremendous interest in recent years in a new class of multi-component metallic alloys that are referred to as high entropy alloys, or more generally, as complex concentrated alloys. These multi-principal element alloys represent a new paradigm in structural material design, where numerous desirable attributes are achieved simultaneously from multiple elements in equimolar (or near equimolar) proportions. While there are several review articles on alloy development, microstructure, mechanical behavior, and other bulk properties of these alloys, then there is a pressing need for an overview that is focused on their surface properties and surface degradation mechanisms. In this paper, we present a comprehensive view on corrosion, erosion and wear behavior of complex concentrated alloys. The effect of alloying elements, microstructure, and processing methods on the surface degradation behavior are analyzed and discussed in detail. We identify critical knowledge gaps in individual reports and highlight the underlying mechanisms and synergy between the different degradation routes. Full article
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